Prosecutors on Thursday said they will not bring criminal charges against Mayor Bill de Blasio after their lengthy investigation into whether people involved in fundraising for his election campaign broke corruption laws.

"After careful deliberation, given the totality of the circumstances here and absent additional evidence, we do not intend to bring federal criminal charges against the mayor or those acting on his behalf relating to the fundraising efforts in question," Acting U.S. Attorney Joon Kim in New York said in a statement.

The investigation examined whether de Blasio and his political team violated state election law by diverting donations to county committees to evade election financing limitations. It also probed whether favors were given or promised in exchange for donations to his 2013 campaign for his political nonprofit, Campaign for One New York, which no longer exists.

Manhattan District Attorney Cyrus R. Vance Jr. released a 10-page letter describing the findings of his office; the disclosure included the fact that de Blasio and his aides could not be prosecuted because they had relied on the advice of their lawyers, and that vague election statues would make it difficult to charge any felonies.

The mayor's office released a statement on the news, saying, "We have been confident from the moment these reviews began that the actions of the Mayor and our Administration have always been within the law," said press secretary Eric Phillips.

He added, "The United States Attorney and Manhattan District Attorney have now put to rest any suggestion otherwise. We thank these prosecutors’ offices for conducting what were clearly diligent and exhaustive reviews — and for making public the conclusions of these probes. New Yorkers deserve honest, progressive government. With this Mayor, they will always get it.”

Yet the mayor and his campaign team did not escape reproach. Vance's letter also criticized the actions as "contrary to the intent and spirit of the laws that impose candidate contribution limits, laws which are meant to prevent 'corruption and the appearance of corruption' in the campaign financing process."